A display device having a light panel such as a liquid crystal display (LCD) panel, brightness of the entire panel should be as uniform as possible. When a backlight is serving as a light source for an LCD panel and the emitted light is non-uniform, frames displayed by the LCD panel will be in a situation of brightness non-uniformity and therefore affecting the user's visual perception.
Conventional methods for measuring brightness uniformity of a panel abide the standard established by the Video Electronics Standards Association (VESA). Brightness uniformity of the entire panel is evaluated as shown in FIGS. 1 and 2 by measuring brightness of 9 points, L1˜L9, or 13 points, L1˜L13, located on the panel. Then, the proportion of the minor to the maximum is calculated so as to obtain brightness uniformity of the panel. However, this evaluation method has the following disadvantages. When only measuring the 9 points or the 13 points of the entire panel, it is probable that brightness of the 9 points or the 13 points is uniform but brightness of the other areas is inconsistent with brightness of those points. By only measuring the 9 points or the 13 points of the entire panel to get a conclusion, saying that brightness of the entire panel is uniform, the conclusion is only a statistical probability and errors may exist. For example, brightness of the 9 points or the 13 points may be adjusted to be uniform, but actually, brightness of the other areas of the entire panel may not necessarily be consistent with brightness of the 9 points or the 13 points. Therefore, by the conventional method of evaluation, brightness of some specific positions of the panel is uniform, while brightness of the entire panel may actually be non-uniform.
The conclusion of the conventional measuring method can be further examined by human eyes. Since judgment of human eyes is subjective, it may result in different judgments due to different observers in different environments. For example, brightness of the 9 points or the 13 points may be uniform, but brightness of the other points may be inconsistent with brightness of the 9 points or the 13 points. When brightness of the entire panel is highly bright, it will be considered as uniform by human eyes due to poor sensibility of human eyes to higher brightness of light. At that time, brightness of the entire panel may actually be non-uniform. By utilizing the conventional measuring method, an unqualified product having non-uniform brightness may be marketed as a result. Because the conventional method for examining brightness of the panel has the aforesaid disadvantages, it is necessary to provide a method to overcome and improve the aforesaid disadvantages of the conventional technique.